before a board of inquiry transmission gully notices of ... · columbia, canada, specialising in...

Statement of rebuttal evidence of Timothy Simon Richmond Fisher

(Sediment Yield Peer Review) for the NZ Transport Agency and Porirua

City Council

Dated: 27 January 2012

REFERENCE: John Hassan ([email protected])

Nicky McIndoe ([email protected])

Before a Board of Inquiry

Transmission Gully

Notices of Requirement and Consents

under: the Resource Management Act 1991

in the matter of: Notices of requirement for designations and resource

consent applications by the NZ Transport Agency,

Porirua City Council and Transpower New Zealand

Limited for the Transmission Gully Proposal

between: NZ Transport Agency

Requiring Authority and Applicant

and: Porirua City Council

Local Authority and Applicant

and: Transpower New Zealand Limited

Applicant

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STATEMENT OF EVIDENCE OF TIMOTHY SIMON RICHMOND

FISHER FOR THE NZ TRANSPORT AGENCY AND PORIRUA

CITY COUNCIL

INTRODUCTION

1 My full name is Timothy Simon Richmond Fisher.

2 I am a Senior Water Engineer and Director at Tonkin & Taylor

Limited (T&T), environmental and engineering consultants of

Auckland. I practise as a civil engineer with specialism in water and

environmental engineering. I am a member of the Institute of

Professional Engineers New Zealand and am a Chartered

Professional Engineer.

3 I have a Bachelor of Civil Engineer (1st Class Honours) and Masters

of Civil Engineering (Distinction) from the University of Canterbury

and a PhD in Civil Engineering from the University of British

Columbia, Canada, specialising in environmental hydraulics. I have

a Diploma in engineering management.

4 I have 17 years of experience in engineering research and

consulting spanning the transport, mining, hydropower, land

development, urban water infrastructure and river management

sectors. I have specialist expertise in hydrology, hydraulics,

stormwater, modelling, water quality and sediment transport.

5 I have extensive experience in the stormwater management,

streamworks and the water quality assessments for major roading

projects and other projects involving large earthworks. Recent

projects that I have been involved with include:

5.1 Huntly Section of the Waikato Expressway (SH1) where I was

the lead author of the stormwater and streamworks

assessment for the scheme assessment report (2011).

5.2 Puhoi to Warkworth (SH1) where I was the peer reviewer of

water reports (hydrology, stormwater, water quality and

erosion and sediment control (ESC)) at the scheme

assessment stage (2011).

5.3 Mt William Mine where I was the reviewer for West Coast

Regional Council of water quality assessment reports at the

pre-lodgement and notification stages (2011).

5.4 Waterview Connection Project (SH20/16) where I was the

stormwater team leader, expert witness for stormwater,

streamworks and flooding issues, and reviewer of modelling

undertaken to assess the effects of sediment on the

Waterview Inlet (2008-2010).

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5.5 Northern Gateway Toll Road1 (NGTR) (SH1) where I was

stormwater team leader and stormwater treatment designer

for the 7.5 km motorway. I was onsite for the four years of

construction and was involved in technical advice to support

the design and operation of ESC systems (2004-2009).

5.6 Manukau Harbour Crossing (SH20) design of stormwater

treatment for resource consents (2007-2008).

5.7 Design and construction of the Mangakotukutuku Stream

diversion2 (1.4 km length) for Solid Energy (2005-2006).

5.8 Water management for the mining industry including

Rotowaro, Maramarua and Ohai mines for Solid Energy,

design and consents for Drury Quarry backfill and stream

diversion for Stevensons, and review of consent applications

for Holcim cement plants/quarries for Otago Regional Council.

5.9 I am currently undertaking reviews of water aspects

(hydrology, stormwater, flooding and ESC) of the MacKays to

Peka Peka (SH1) project for the Environmental Protection

Agency.

6 I offer the Board my advice based on my extensive experience with

water aspects of larger roading and earthworks projects and with

the advantage of my overview across all the water assessments in

my role as peer reviewer for the NZ Transport Agency (NZTA).

7 I am the reviewer of water aspects of the Project for NZTA that were

summarised in Assessment of Water Quality Effects Report

(Technical Report 15) and Assessment of Hydrology and Stormwater

Effects (Technical Report 14). I am the author of Transmission

Gully Project – Peer Review of Sediment Yield Aspects (19

December 2011). I was the author or reviewer of four working

review reports provided to NZTA during the development of

Technical Reports 14 and 15.

8 My evidence is given in support of the NZTA and Porirua City Council

(PCC) Project components of the Transmission Gully Proposal

(together the TGP or the Project). It does not relate to the

Transpower Project.

1 Winner of Association of Consulting Engineers Innovate Gold award for projects that

show excellence in technical skills, interaction with the client and team members and innovation. Winner of IPENZ Arthur Mead Award (Merit) for projects that best

exemplify sustainable management of resources and care for and consideration of

environmental values.

2 Winner IPENZ Arthur Mead award. Winner of Innovate Silver Award.

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9 I am familiar with the area that the Project covers and the streams,

Porirua Harbour and topography in the vicinity of the Project. I have

visited the site.

10 I have read the Code of Conduct for Expert Witnesses as contained

in the Environment Court Consolidated Practice Note (2011), and I

agree to comply with it as if this Inquiry were before the

Environment Court. My qualifications as an expert are set out

above. I confirm that the issues addressed in this brief of evidence

are within my area of expertise. I have not omitted to consider

material facts known to me that might alter or detract from the

opinions expressed.

SCOPE OF EVIDENCE

11 My evidence will deal with the following:

11.1 Executive summary;

11.2 Background and role;

11.3 Existing sediment yield;

11.4 Construction sediment yield;

11.5 Managing uncertainty and risk; and

11.6 Proposed conditions.

12 My statement of evidence responds to submitters evidence by:

12.1 Dr Basher on behalf of Department of Conservation (DOC);

12.2 Mr Handyside on behalf of DOC; and

12.3 Ms Helen Kettles on behalf of DOC.

13 Those witnesses refer to my Peer Review of Sediment Yield Aspects

(19 December 2011) and peer reviews of earlier draft documents.

In order to present a complete picture, this statement describes my

work carried out, but only on sediment yield aspects.

14 Related to that, my statement of evidence also considers the

evidence by:

14.1 Ms Malcolm (both evidence in chief and rebuttal);

14.2 Mr Gough (evidence in chief and rebuttal); and

14.3 Mr Pathmanathan Brabhaharan (rebuttal).

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15 I have reviewed the conferencing statements relevant to my area of

expertise, and comment on these where appropriate.

16 While I have reviewed Dr Hicks Section 42A Report dated January

2012, I have not had sufficient time to thoroughly comment on that

report in this evidence. Nor have I had an opportunity, at the time

of preparing this statement, to consider the Section 42A Report

which I understand is being prepared by Gregor McLean. I

understand there will be opportunities for me to comment on these

reports either in future evidence or at the hearing itself.

SUMMARY OF EVIDENCE

17 My evidence discusses the sediment yield aspects of Technical

Report 15.

18 The revised estimate of construction sediment yield3 provides a

better estimate than that provided in Technical Report 15 because

greater detail was considered in the assessment of USLE factors. I

consider the revised construction sediment yield to be suitable for

the assessment of effects. On the basis that the revised construction

sediment yield is higher than the estimates in Technical Report 15,

the values used in the assessment of ecological effects are

appropriate, subject to consideration by ecologists of the uncertainty

and the change of effects in the Kenepuru and Pauatahanui

catchments.

19 There remains uncertainty with regard to the estimates of baseline

and construction sediment yield estimate. This uncertainty is better

understood as a result of the rebuttal evidence of Ms Malcolm,

which includes statements on the uncertainty, sensitivity, and

potential conservatism in the construction sediment yield.

20 This uncertainty is inherent in sediment assessments for

construction projects and not different to other roading/earthworks

projects and consent applications that I have seen.

21 To manage remaining uncertainty, the focus needs to be on consent

conditions that:

21.1 Confirm the basis for the consent application (assumed

sediment yield and effects);

21.2 Minimise the uncertainty and risks by applying best practices

for ESC; and

3 SKM (20 January 2012) Revised Analysis attached to Expert Conferencing Joint

Report to the Board of Inquiry – Earthworks & Sediment Control Conferencing, 20 January 2011.

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21.3 Require monitoring and adaptive management that ensure

that specified performance from construction and sediment

and erosion practices are achieved.

22 I recommend additional consent conditions to manage the

uncertainty and provide confidence to the Board of Inquiry.

BACKGROUND AND ROLE

23 NZTA engaged T&T in 2010 to undertake peer review of SKM and

DHI work on water aspects of the Project. These reviews covered

the full suite of water assessments that form the basis of Technical

Reports 14 and 15. Reviews were undertaken in October 2010 of

early assessment reports and then in May 2011 of draft versions of

Technical Reports 14 and 15. These peer reviews are listed below

as they are at times referred to by other witnesses:

23.1 T&T “Peer review of Draft modelling of sediment in the

streams and harbours” (20 October 2010);

23.2 T&T peer review “Transmission Gully – Workstream 12 – Peer

Review” (29 October 2010) which reported on review of

“Erosion and Sediment Control Philosophy”, “Sediment Yield

Calculations” and “Construction and Erosion and Sediment

Control” reports;

23.3 T&T “Transmission Gully – Peer Review of Water Quality

Assessment of Effects” (Draft, 5 May 2011); and

23.4 T&T “Transmission Gully – Peer Review of Hydrology and

Stormwater” (Draft, 13 May 2011).

24 In December 2011 NZTA asked me to finalise the peer review of the

sediment yield aspects of Technical Report 15. The purpose of the

peer review was to provide an independent opinion to NZTA on the

specific sediment yield aspects including sediment modelling and

sediment retention/ control assumptions. The report gave

consideration to the evidence of Ms Malcolm and Mr Gough,

Submitter 43 (Department of Conservation) and the expert caucus

statement 7/8 December 2011. This peer review is titled:

24.1 T&T “Transmission Gully Project – Peer Review of Sediment

Yield Aspects” (19 December 2011).

25 In anticipation of the need to prepare this evidence I participated in

the conferencing of Earthworks & Sediment Control experts on

20 January 2012.

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EXISTING SEDIMENT YIELD

USLE method

26 The USLE4 method was used as the basis for the sediment yield

assessment. The method has a number of limitations including that

it is not calibrated for New Zealand conditions, it estimates average

annual sediment loss rather than events or unusual wet/dry

seasons, and is not able to accurately estimate the absolute

sediment yield. Its strength is in identifying hotspots for sediment

generation and where ESC efforts should be directed.

27 Despite the limitations with the USLE method, it remains the most

commonly applied method in New Zealand for assessing the

sediment yield and for designing sediment and erosion control

systems for engineering/development projects involving earthworks.

28 Dr Basher5 expresses considerable concerns with the USLE as it

does not represent landslides and bank erosion, it was not

developed for such steep terrain and it predicts average annual soil

loss that then requires temporal downscaling. These points are all

valid and I have made similar points in the past (T&T, 29 October

2010). However, by scaling to the SSYE6 estimate as has been

done for the Project, the USLE essentially becomes a SSYE estimate.

The perseverance with the underlying USLE model enables the

change in sediment estimate due to construction activities to be

assessed.

29 I accept Dr Basher’s opinion that other sediment generation models,

such as GLEAMS, are better than the USLE method, particularly

because of their temporal modelling e.g. direct modelling of events

or long term simulations. I have made a similar point in the past

(T&T, 29 October 2010). Although, it is important to note that other

sediment models also have their limitations as is recognised by Dr

Basher7 and Dr Hicks8 and limits on their suitability for this Project

(e.g. GLEAMS requires more detail).

30 Ms Malcolm9 makes the point that the USLE modelling approach is

pragmatic and suitable for a construction design that is not fully

developed as is the case for the Project. USLE is suited for such an

approach, whereas alternative models such as GLEAMS require more

detail of the construction methodology and ESC practices.

4 Universal Soil Loss Equation.

5 Dr Basher evidence in chief paragraphs 7, 29-35.

6 Suspended Sediment Yield Estimator developed by NIWA.

7 Dr Basher evidence in chief, paragraph 60.

8 Dr Hicks Section 42A Report dated Jan 2012 Section 3.4

9 Ms Malcolm evidence in chief, paragraph 119.

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31 The Project has adopted a broad approach to construction design of

defining the maximum working areas, outlining the ESC philosophy

and broad plans. Examples of what the erosion and sediment plans

might look like are detailed in six separate Site Specific

Environmental Management Plans (SSEMPS). In general I agree

with this approach because it has been my experience with large

earthworks projects that detailed environmental management plans

and ESC plans change as a result of detailed design and

construction methodologies that a contractor brings to the project10.

I consider that prescribing a detailed construction methodology via

the consent process will reduce the ability of the contractor to

optimise and innovate to reduce Project cost and improve

performance (including that of ESC systems). My agreement to this

approach is conditional on the adequacy of the ESC philosophy,

assumed treatment efficiencies and the example SSEMPs to set a

benchmark for construction and to prove that ESC standards in

difficult areas can be achieved.

32 I accept Ms Malcolm’s point11 that a lumped model rather than one

that resolves all of the processes is suitable. The USLE and SSYE in

the way that they are applied are essentially lumped models

estimating sediment yield at point (harbours).

33 The caucusing statement of 7/8 December 2011 recognises that the

USLE is the best method for estimating the sediment yield from

construction for the Project1213.

34 It is my opinion that, on balance, the USLE (scaled to the SSYE)

sediment model can provide suitable sediment estimates and is

adequate for the assessment, provided that specific technical inputs

such as USLE factors are correctly applied and reasonable

assumptions are made for staging and ESC practices.

Existing sediment yields

35 The simulation of existing sediment yields and transport/distribution

was undertaken to provide a context (baseline) for the assessment

of construction effects due to sediment.

36 Overall, the modelling provides a suitable estimate of the existing

sediment yields and the transport/distribution of sediment in the

receiving environments. This is achieved largely by scaling the

USLE estimates to be similar to those estimated by the more

10 Mr Gough notes similar experience and cites similar views from Ms Rickard and

Mr Handyside. Refer to Mr Gough rebuttal evidence, paragraph 19.

11 Ms Malcolm evidence in chief, paragraph 106.

12 Expert Conferencing Joint Report to the Board of Inquiry – Earthworks & Sediment

Control Conferencing, 7&8 December 2011, paragraph 14.

13 Caveats to this statement are made by Dr Basher in his evidence in chief paragraph 71d.

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accurate NIWA suspended-sediment yield estimator (SSYE). I have

confidence in the estimate of existing sediment yields due to the

following key steps in the modelling methodology:

36.1 The sediment yield model based on the USLE model was

scaled14 to the SSYE by adjustment of the sediment delivery

ratio (SDR). The SSYE is considered to be the best available

tool for estimation of suspended sediment for catchments in

New Zealand. The caucusing statement of 7/8 December

201115 recognised that the SSYE is the best model for

providing the baseline sediment estimates.

36.2 The sediment yield model was validated using Healy (1980)

observations with reasonable explanations for differences.

The limitations of this validation are noted by Dr Basher,16

and I accept he is correct in noting this.

36.3 The sediment rating curves were created to temporally

distribute the sediment to allow for subsequent analysis

(event and long-term simulations). These were validated by

comparison to observed suspended sediment data for

Horokiri, Pauatahanui and Porirua catchments. The caucusing

statement of 7/8 December 201117 states agreement that the

sediment rating curves are a good fit to observed data for the

Horokiri and Porirua catchments and appear to overestimate

(conservative) for the Pauatahanui catchment. I note

Dr Basher’s concerns18 with the methodology and

implementation of this step and Ms Malcolm’s rebuttal19 of

these issues.

36.4 The hydrological models that were used to create the

sediment rating curves were also calibrated.

36.5 Stream modelling was undertaken with HEC RAS20 models

using calibrated inflows but with not hydraulic calibration.

Observations of natural bed material were relied on for

qualitative verification. I note that the sediment yields used

14 It is more appropriate to describe this process as scaling than calibration as pointed

out by Dr Basher (evidence in chief paragraph 71a) as measured data is required for calibration.

15 Expert Conferencing Joint Report to the Board of Inquiry – Earthworks & Sediment Control Conferencing, 7&8 December 2011, paragraph 10.

16 Dr Basher evidence in chief, paragraph 71b.



18 Dr Basher evidence in chief, paragraph 51-56.

19 Ms Malcolm rebuttal Appendix B.

20 HEC- RAS (Hydrologic Engineering Centers River Analysis System) is a 1-D hydraulic model produced by the United States Army Corps of Engineers.

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for the stream modelling are those for the end of streams (at

harbours), but believe this to be appropriate21 as the USLE

estimates (scaled to SSYE) do not account for any retention

of sediment in streams. The results from the stream

modelling are not used for the harbour modelling.

36.6 Harbour modelling undertaken with the DHI MIKE suite of

models provide current best practice for the hydrodynamic

modelling. The harbour modelling was reviewed by T&T

(20 October 2010) and T&T (05 May 2011). The harbour

model was reasonably calibrated to field observations

(although with some limitations noted, which are considered

to be reasonable). Verifications are based on qualitative

comparison to observed historical sedimentation.

36.7 The sediment modelling suite (all models) predicts

accumulation in the harbours that is comparable to

historically observed sedimentation rates with reasonable

explanations for differences. . Therefore, the sediment

modelling suite provides an adequate simulation of the

baseline to enable the effects of the Project to be modelled.

CONSTRUCTION SEDIMENT YIELD

37 The most critical aspect of all the water assessments I have

reviewed is the estimation of sediment yields from the construction

sites22. The addition of sediment from the Project, over and above

the existing catchment sediment yields, is the change that causes

the greatest potential for effects on the environment. This was

agreed in the expert caucusing of 20 January 2012, where “the key

issue for all participants of the meeting is the difference between

the baseline and construction yield estimates”23.

38 The process I followed for my peer review of the construction

sediment yield and repeat here is to review the suitability of the

method, review the underlying assumptions, check the sediment

yields are reasonable and comment on the uncertainty. I comment

21 In my peer review report 19 December 2011, I noted that the sediment estimate

used for the stream modelling may be an underestimate due to in stream process.

This was used by Dr Basher in his evidence in chief paragraph 71c as support for his view that there was an underestimation of sediment supply to streams. I now

recognise that the sediment estimate (USLE based scaled to SSYE) does not

account for any sediment retention in the steam because this process is not

included in the SSYE, so that the sediment estimate used for the stream assessment is appropriate.

22 T&T Peer Review 29 October 2010 page 3.

23 Expert Conferencing Joint Report to the Board of Inquiry – Earthworks & Sediment Control Conferencing, 20 January 2012, paragraph 7.

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on how these issues have been addressed in the USLE Revised

Analysis24 and the revised sediment estimate in that report.

USLE Methodology

39 The suitability of the USLE methodology was covered above. The

application of the method is covered here. In Technical Report 15

the USLE was applied broadly for the Project, for example,

earthwork areas were based on a 75 m working corridor. In the

USLE Revised Analysis the land area and factors were calculated

every 10 m, for example the earthworks areas were based on the

design widths with allowances for coincidental works to construct

stream diversions, access roads and fill sites. The allowance for

earthworks to construct the stream diversions was based on 20 m

width (Mark Edwards, caucus meeting 20 January 2012). The

greater detail that was used for the revised sediment estimate

results in a better estimate25.

USLE Assumptions

40 The USLE assumptions and factors have a significant impact on the

estimates of average annual sediment yield. Issues identified by

the review process are now covered.

41 K factor (soil erodibility) used in the USLE model is based on surface

soil types. The caucusing statement of 7/8 December 2011

recognised that the K factor in the construction scenario is

conservative because in the construction scenario there is less

erodible material26. In my peer review I highlighted that some of

the earthworks will occur in rock, which would likely reduce the

sediment yield estimates. In the USLE Revised Analysis the

proportion of the earthworks in rock is accounted for in the K factor.

Mr Brabhaharan assisted by providing much more detailed

information on the rock component of the earthworks material.

Overall, 70% of the estimated available cut volume is estimated to

be in rock. This significantly reduces the K factor and acts to reduce

the revised sediment estimate.

42 LS factor (length slope and steepness factor) has been more

accurately assessed in the USLE Revised Analysis based on design

cross-sections. There are a couple of limitations on how the LS

factor has been applied. The first limitation is that the design cross-

section for the finished road was used, whereas in reality there are

multiple, different cross-sections that occur during construction.

The second limitation is the arithmetic averaging that is used to

24 USLE Revised Analysis (20 Jan 2012) by SKM attached to Expert Conferencing Joint

Report to the Board of Inquiry – Earthworks & Sediment Control Conferencing, 20

January 2012


Control Conferencing, 20 January 2012, paragraph 8.


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determine a LS factor for each 10 m cross-section may skew the LS

factor. These simplifications are pragmatic and appropriate for the

accuracy of the USLE method. The USLE Revised Analysis report

says that the revised LS factors are generally similar to the

Technical Report 15 factors, although the revised LS factors have a

greater range of variability.

43 C factor (cover) is unchanged in the USLE Revised Analysis with the

exception of Ration, which is assumed to only have earthworks for

nine months. P factor (erosion control practise) was unchanged in

the USLE Revised Analysis.

44 The application of SRE (erosion removal efficiencies) is confused in

Technical Report 15 due to inconsistencies and contradictory

information. This has been clarified in the USLE Revised Analysis,

which says that that Technical Report 15 estimates did not allow for

erosion control, but only included sediment removal that was

applied to remove 70% in the Q2 and Q10, and 40% of sediment in

the Q50.

45 The USLE Revised Analysis accounts for both erosion control and

sediment controls. Erosion control is applied by proportioning the

earthworks areas as being stabilised, under erosion control or as

active earthworks. Sediment control is applied to erosion control

and active earthworks areas. The net effectiveness of the erosion

control and sediment controls is demonstrated in Table 1. The

inclusion of erosion control measures acts to decrease the revised

sediment estimate.

Table 1: Net effectiveness of erosion and sediment control

measures.

Erosion Control

Active

Earthworks

Erosion

Control

Stabilised

0%

erosion

control

75%

erosion

control

100%

erosion

control

Sedim

ent

Contr

ol

Chemical

Treatment

Ponds 3%

70% Q2

and Q10

removal

rate

70% 92.5% 100%

Other

Sediment

Devices

30%

removal

rate

30% 82.5% 100%

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46 A SDR factor (sediment delivery ratio) of 0.17 was applied in

Technical Report 15 to scale the USLE sediment yield to that

predicted by the SSYE. I accept the process of global scaling of the

USLE estimate to be similar to the SSYE estimate. However, using

the SDR for this scaling is problematic as this global scaling

accounts for processes other than “sediment delivery”. This

becomes a problem for the construction sediment estimate, when a

different SDR may be appropriate for the construction areas versus

the unchanged areas of the catchment. Ideally a new separate

global factor should have been introduced to separate the global

scaling of USLE to SSYE to the SDR factor representing sediment

delivery “processes”. Technical Report 15 describes how very little

sediment is retained in the streams, suggesting a high SDR factor

would have been appropriate, if separated from the global scaling.

47 Dr Basher27 is critical of the downscaling using the SDR because the

same SDR value is used for construction areas. As a minimum he

believes that the modelling should be re-run using a more

conservative SDR factor of 0.5 or 0.7 depending on slope

steepness28. The caucusing statement 7/8 December 2011

recognised that using the same scaling factor that has been applied

to the overall catchment to the construction area does not account

for the higher connectivity of construction sites to receiving

environments29. In my peer review30 I suggested that values lower

than 0.5/0.7 would be justified to allow for sediment losses

(detention) in streams31. I accept that there is little sediment

detention in the streams based on evidence to this effect in

Technical Report 15 and that values of 0.5/0.7 are appropriate for

earthworks areas. Therefore, the Technical Report 15 estimates of

sediment yield from construction areas from the SDR assumption

alone are likely to be low.

48 Auckland Council32 suggests for earthworks sites SDR values of 0.5

should be used, increasing to 0.7 for slopes steeper than 10%. The

USLE Revised Analysis uses SDR values of 0.5 and 0.7 for steeper

catchments. This increase in the SDR factor acts to increase the

revised sediment estimate.

27 Dr Basher evidence in chief paragraph 8-10, 39-50.

28 Dr Basher evidence in chief paragraph 17.


30 Dr Fisher peer review of sediment yield aspects, 19 December 2011, Section 3.3.3.

31 This view was challenged by Dr Basher in his evidence in chief, paragraph 71.e.

32 Auckland Council (2011) Module 3 – Erosion and sediment control: Workshops for

plan preparers. Prepared by Erosion Management Ltd and Environmental Communications Ltd.

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49 The revised sediment estimate that results from the USLE Revised

Analysis is lower overall than the Technical Report 15 estimate.

While, the higher SDR factors have increased the sediment yields,

the lower K factors and inclusion of erosion control measures cause

the revised sediment estimate to be lower overall.

50 The total of the Q10 estimates33 for the revised approach is 27%

lower than the Technical Report 15 estimate. For the Kenepuru and

to a lesser extent the Pauatahanui the revised sediment estimates

are higher, which Ms Malcolm addresses in her evidence34. On this

basis, the assessment of ecological effects that uses the higher

Technical Report 15 values is appropriate, subject to consideration

of uncertainty and the change of effects in the Kenepuru and

Pauatahanui catchments.

Sediment yields

51 The sediment yields from construction areas should ideally be

validated against measured sediment data from other locations.

However, there is a lack of measured data in the Wellington region

and sediment yields do vary widely with different site conditions,

which make validation difficult. Mr Brabhaharan35 says that based

on his experience in the Wellington region and knowledge of the

Project geology that “...the sediment generated from the earthworks

associated with TGP, is likely to be significantly less, compared to

major earthworks project in Auckland.” I make comments below on

the use of monitoring during construction to validate the estimated

sediment yields.

Uncertainty

52 Uncertainty in the sediment estimates was identified in my peer

review. In his evidence Dr Basher considers this uncertainty to be a

major issue. The caucusing statement of 20 January 2012

recognises that the revised sediment estimate provides a better

estimation and a reduced uncertainty in the USLE parameters36.

However, uncertainty remains, which is inherent in the methods

used and more generally in sediment science.

53 I consider that the uncertainty in the sediment modelling suite

detailed in Technical Report 15 occurs in a number of areas:

53.1 SSYE baseline

53.2 USLE method and factors

33 Ms Malcolm rebuttal evidence, Table 1.

34 Ms Malcolm rebuttal evidence, paragraphs 21 and 25.

35 Mr Brabhaharan rebuttal evidence paragraph 9.5.


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53.3 Construction methodologies and ESC effectiveness

53.4 Transformation of sediment yields to harbour and stream

models

53.5 Assessment models (HEC RAS stream models and MIKE21

harbour model).

54 Ms Malcolm addresses the uncertainty in her rebuttal evidence37.

More data would help to confirm the SSYE baseline and I

recommend that this should be done prior to construction.

However, the uncertainty would still remain in many components of

the construction sediment estimate. I comment further on

managing this uncertainty in the following section.

MANAGING UNCERTAINTY AND RISK

55 All the sediment experts recognise the uncertainty with the

construction sediment estimates based on the USLE method. I

consider that there is uncertainty in the assessment and risk of poor

performance during project delivery and I treat these separately.

56 As a general comment the focus needs to be on management (of

mitigation measures), monitoring and responses to manage/reduce

the uncertainty. These need to be captured in consent conditions. I

agree with Dr Basher that if the applications for construction of TGP

were to be granted then conditions for ESC would need to be very

stringent and monitoring of performance, reporting and potential for

reviewing management approaches swiftly and comprehensively38.

Uncertainty in the assessment

57 Uncertainty is inherent in the estimation of sediment yields in

general and more so for construction sites. This uncertainty is

common to all similar projects and consent applications. A

precautionary approach is required for the Project given the scale of

the earthworks and the sensitivity of the receiving environments.

However, the Project has gone as far as any project that I have

been involved with to quantify the sediment loads and the

uncertainty associated with these. There is not much more that can

be done using the methods that SKM have employed for Technical

Assessment 15 and the additional work detailed in the Revised USLE

Analysis and uncertainty/sensitivity assessments in the rebuttal

evidence of Ms Malcolm. The risk that the sediment yields and

effects are different to those that have been assessed can be

managed by the conditions of consent that have been proposed and

with additional consideration of the conditions that I propose in my

evidence.

37 Ms Malcolm rebuttal evidence, Appendices A and B.

38 Dr Basher evidence in chief, paragraph 17.

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58 I would recommend pre-construction monitoring of sediment in the

key streams affected by the construction of the Project to confirm

the existing sediment loads and the baseline environmental

conditions. Dr Basher39 agrees with this approach and says that the

checks should be in relation to the sediment rating curves as this is

all that can be checked. The checks should be to ascertain whether

the sediment rating curves are in the right “ball park” and should

focus on the catchments for which sediment rating curves were

derived without the benefit of local field measured data.

59 Concern has been expressed by myself and Mr Handyside during

caucusing about the ability of sediment ponds to remove 70% of

sediment during the Q10 event. I note Mr Gough’s replies to this

issue40. While there is sufficient evidence in Moores and Pattison

(2008) and the general literature to support the 70% pond removal

efficiencies for normal events used for the SRE, there is no data to

quantify the removal efficiencies for extreme events.

60 On this basis, the sediment estimates for the 10 year return period

events and higher have greater uncertainty and may be higher than

estimated. If this is an area of uncertainty then the consequence of

this should be understood, which is the point of Ms Malcolm’s

sensitivity assessment41. The adaptive management approach and

performance monitoring as described below are the best and only

course of action to manage the uncertainty regarding this issue of

pond performance.

61 Mr Gough advises that the sediment control efficiencies of sediment

control devices other than ponds (e.g. super silt fence, biosock and

decanting earth bunds) will have removal efficiencies that are

greater than the 30% than has been assumed in the USLE Revised

Analysis. Therefore, the revised sediment estimate may be

conservative in this area, although this only affects 5-20% of the

Project by area42.

62 The Project proposes extensive monitoring of ESC systems. These

are detailed in Appendix 15.L of Technical Report 15 (which is also

attached to the draft43 Construction Environmental Management

Plan in volume 5 of the application documents). The proposed

monitoring includes inspections of erosion control, surface water

control and sediment control, which are standard practices. The

Project also proposes performance monitoring of sediment control

39 Dr Basher evidence in chief, paragraph 71f.

40 Mr Gough rebuttal evidence, paragraph 25.

41 Ms Malcolm rebuttal evidence, Appendix A.

42 USLE Revised Analysis (20 January 2011), Table 11.

43 The consent conditions require draft plans to be updated and finalised.

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devices and at catchment control points, which are significant

additional measures that I have not seen on a project before.

63 The performance monitoring measures are part of an adaptive

management approach that the Project proposes44. But these have

the secondary benefit of confirming the assumptions in the

assessment of effects. Should the measured sediment yield be

greater than that assumed in the assessment of effects, then

measures would need to be implemented to assess the actual effect

or to reduce the sediment yield. Such measures to reduce the

sediment yield could include more stringent ESCs including

improvements to the sediment pond designs (larger or changes to

chemical systems) or provisions for reduced earthworks area.

64 To respond to concerns raised by Dr Basher and Mr Handyside, I

understand the NZTA and PCC propose that a Sediment

Management Peer Review Panel be established using independent

professionals to support NZTA and the Greater Wellington Regional

Council in the management of ESC practices. A role of this panel

would be to review pre-construction monitoring and construction

performance monitoring. I have seen such panels successfully

operate in respect of mining operations (where water quality was

also a critical issue) and would support this proposal. I understand

that Ms Rickard will draft and circulate consent conditions for

consideration as part of the upcoming combined planner and

sediment engineering conferencing session. I have provided some

thoughts to Ms Rickard on the drafting of this.

65 There was concern expressed during caucusing of 20th January 2012

that the sediment generation from stream diversions is not well

quantified. More information is available on the stream diversions in

the report Diversion Staging Physical Design Parameters & Adaptive

Management that is appended to the Ecological Management and

Monitoring Plan.

66 Ms Malcolm addresses the issues of sediment generation from

stream diversions in her rebuttal evidence45. I agree with her that

the earthworks activities associated with the stream diversion are

included in the revised sediment estimate. I agree with her that the

sediment generated from the stream works within wetted stream

channels cannot be estimated using the USLE method and I know of

no reliable method to estimate the sediment from this source.

67 I consider that the sediment generation from stream works within

wetted stream channels to be relatively minor (compared to Project

earthworks activities), provided that the new stream channel is

44 Refer to the Ecological Management and Monitoring Plan page 35 for the principles

of the adaptive management approach.

45 Ms Malcolm rebuttal evidence, Appendix B.

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properly stabilised and the diversion of the stream into the new

stream channel is quickly and carefully orchestrated. My view is

based on my experience with stream diversions made for the

Mangakotukutuku Stream diversion and for temporary diversions to

allow for the construction of culverts on the NGTR. In the case of

the Mangakotukutuku Stream diversion some suspended sediment

was added to the stream water due to earthworks to open the

upstream end of the diversion and from dust washed out of the

rocky substrate forming the bed of the new stream channel. This

suspended sediment discharge was relatively minor and equivalent

to the sediment concentrations experienced during high flows in the

stream, but it occurred for a much shorter duration (less than one

hour).

68 I have reviewed the proposed consent conditions that cover the

physical quality, sediment management and implementation of

streamworks including G.15(A), G.15(D), WS.1, WS.2, WS.3 and

WS.4. Based on my experience drafting the streamworks consent

conditions for the Waterview Connection project, I believe that the

consent conditions controlling streamworks should be more explicit

in a number of areas:

68.1 Inclusion of stream diversion plans in the requirements of the

SSEMPs, which is implied by the content of the example

SSEMPs but the inclusion of this as a consent condition

removes all doubt.

68.2 Inspection of the stream diversion by appropriately qualified

and experienced engineer and ecologist to certify that the

streamworks have been undertaken in accordance with the

drawings and plans within three months of completion of the

streamworks.

69 Ms Malcolm46 in her sensitivity assessments demonstrates the

importance of erosion and sediment control measures working

together. In her Scenario 1 the lower performance of sediment

controls (e.g. ponds and other devices) is offset by accounting for

deployment of erosion control measures when heavy rain is

forecast. The effectiveness of additional erosion control measures

deployed on the basis of forecast rain was not considered in the

Technical Report 15 estimates, or in the revised sediment estimate.

Therefore, the sediment yields are conservative in this regard. This

approach is a requirement of consent condition E.3(j), which

requires that all practicable erosion and sediment control measures

are put in place if a stabilisation trigger event47 is forecast.

46 Ms Malcolm rebuttal evidence, Appendix A.

47 The stabilisation trigger event is described in Mr Martell’s rebuttal paragraphs 21-25.

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Risks during construction

70 There is also uncertainty that comes from the implementation of

ESC practices. Whilst these are uncertainties, I note that managing

these aspects on construction sites is increasingly standard practice.

71 The risks are greater for the Project due to the difficult terrain and

sensitive receiving environments. However the proposed consent

conditions, including an adaptive management approach based on

the proposed performance monitoring, provide strong measures to

manage this risk.

72 A specific measure to reduce the risk during heavy rainfall is the

deployment of erosion control measures in anticipation of a storm

(as mentioned previously in paragraph 69).Requirements for these

actions are included in the proposed consent conditions. This

approach will partially mitigates the risk of poorer pond performance

during extreme events.

73 Uncertainty has been created in the consent application by the lack

of ESC detail to support the ESC aspects of the Site Specific

Environmental Management Plans. This concern was expressed with

regard to Te Puka by Mr Handyside48 and reiterated by him in

caucusing4950. I have recommended to NZTA that additional work is

done in this area to report back to conferencing of Earthworks &

Sediment Control experts. I believe that extra detail will provide

confidence on the practicalities of construction of some of the works

e.g. Te Puka stream diversions and provide greater confidence in

the assessment of construction sediment load.

74 The adaptive management approach supported by monitoring (both

inspection and performance monitoring) provides mechanisms for

feedback and continuous improvement of ESC to ensure that they

met the performance standards set by condition E.3A. The addition

of a Peer Review Panel into the adaptive management framework

will provide additional robustness to this process.

75 The greatest risk of excess sediment comes from poor onsite

practices, which the controls that are proposed for the Project are

designed to prevent. A second risk is from failure of ESC devices

that work well for normal conditions, but are unable to cope with

extreme events (up to and beyond the design events). This risk

increases for steep terrain and for larger sites (as getting the detail

right everywhere over a wider area requires extra diligence and

vigilance).

48 Mr Handyside evidence in chief, paragraph 42.




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76 My experience from the NGTR in similarly steep terrain with 4

million m3 of earthwork is worth considering. The NGTR is

considered to be a case study for good ESC practice, but there were

still failures of devices, although without any environmental

consequences. Such failures were due to small construction details

being wrong, which are only exposed in extreme weather and that

can result in a cascading of consequences. For example, a diversion

channel overtops due to a low point in the bank or it breaches,

which adds more catchment and flow to a pond (over and above

what it was designed for) causing flow over the spillway to exceed

design flows, and partial washout of the spillway. Careful checking

and implementation of ESC practices is required. Consideration of

the performance of ESC devices for what could go wrong may lead

to better, more robust ESC practices.

77 Inclusion in ESC plans of risk assessments and with consideration of

the specific risks to the receiving environment and what could go

wrong with ESC systems would add rigor to the ESC planning. It is

recommended that risk assessments be included as a requirement

of condition E.5.

78 Independent checking of ESC practices is considered to be good

practice for earthworks sites. Frequent inspections are necessary,

but if these are undertaken by the same individuals, then their

benefit may diminish. Periodic review of the ESC practices by

independent professionals (with fresh eyes) can identify issues

and/or offer alternative approaches. It is recommended that this

independent checking role be undertaken by the Sediment

Management Peer Review Panel.

79 Education and performance incentives to contractors for good ESC

practice also can make a difference. I note and support the

condition G.12(A) that Ms Rickard has included for training of

contracting staff on construction and maintenance of ESC devices

and in the details of stream diversions. An example of performance

incentives is the construction of the NGTR where a key result area

was based on performance scoring by the Auckland Regional Council

during its weekly walkovers of the site to inspect the ESC systems.

Good performance in this key result area was linked to performance

bonuses for the alliance that delivered the project. The use of

performance measurements linked to incentives for the NGTR

helped to drive the excellent performance of the erosion and

sediment systems.

CONSENT CONDITIONS

80 I understand Ms Rickard is coordinating revisions to consent

conditions for discussion with the Earthworks and Erosion Control

Expert Caucusing group. With regard to the conditions of consent

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that are appended to her rebuttal evidence I wish to make the

following points (some carried down from my evidence above):

81 I recommend before construction that additional baseline monitoring

of sediment in the key streams affected by the construction of the

Project be carried out to confirm the existing sediment loads and the

baseline environmental conditions for performance monitoring

control stations.

82 I recommend monitoring of sediment removal efficiencies and

sediment discharged to streams at control locations is required to be

undertaken to validate the Project assumptions and predicted

construction sediment yields. This is already a requirement of the

ESC monitoring plan (15L) and is partly covered by conditions

G.15(A).b.v and E.14 to E.16, but the differences should be

reviewed and reconciled if important.

83 I recommend a Sediment Management Peer Review Panel be

established using independent professionals to support NZTA and

the Greater Wellington Regional Council in the management of ESC

practices. This is considered to be beneficial due to the large

amount of monitoring to be undertaken and application of the

adaptive management approach, which may at times require

independent, expert advice.

84 I support area limits on active earthworks, but recommend that

these be changeable based on performance monitoring. This could

be achieved by including them in the ESC plans. The changes to

these would require review and recommendation from the Sediment

Management Peer Review Panel and approved by Council Manager.

85 I support the proposed adaptive management approach (consent

condition E.3(l)), but believe that more clarity is required on how

this process will work.

86 I recommend inclusion in ESC plans of risk assessments requiring a

change to condition E.5.

87 I recommend that consent condition E.19(c) include the specific

requirement for bench testing using the proposed flocculants, which

I understand to be the intention of the condition but this would

make it clearer and avoid doubt.

88 I recommend that the definition for the stabilisation trigger event

(e.g. mm of rainfall in a specific period) be defined in the conditions

of consent.

89 I believe that the consent conditions controlling streamworks should

be more explicit in a number of areas;

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